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#1
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Power supply question
I'm in the process of building a dual purpose power supply. The supply
will have two outputs. One will be 24VAC rated at 4.0 A. The load on this supply will probably never exceed 2.0 A. The second supply will consist of a bridge rectifier off the 24V tap connected to a suitable filter cap of say 1000UF. This filtered DC will then be connected to a small surplus 12V regulator board and heat sink assembly which by the looks of it can handle 5A or better. I plan on mounting this regulator in the cabinet and providing a terminal strip for the 12V output. The DC load will probably never exceed .500 - .750 A. Now here is the dilemma. I haven't tried to put all this together yet, but I know that once I rectify and filter the 24VAC I'll probably end up with something like 30VDC out. The regulator uses a ua723, a TO3 and a smaller TO transistor as well a whole bunch of discrete components. I have no specs on this regulator, but it is well built, appears to be commercial grade, and although it might handle it fine I'd feel a lot better hitting it with something like 18VDC instead of 30. I would hate to blow it up trying to see if it would work on the higher input. I could add some series resistance either before or after the bridge, but the voltage drop across this resistance would vary depending on the total load and I'm not sure how well such a scheme would work. So I was thinking about employing a voltage divider at the output of the filter. The resistance ratio would be easy to figure out, however I'm just not sure how to determine the optimum resistor values. Does this seem like a viable plan, or perhaps someone my have other thoughts as to how to address this? If someone could please help me with this I would be very grateful. Thanks, Lenny |
#2
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Power supply question
On 2/18/2013 9:49 AM, klem kedidelhopper wrote:
I'm in the process of building a dual purpose power supply. The supply will have two outputs. One will be 24VAC rated at 4.0 A. The load on this supply will probably never exceed 2.0 A. The second supply will consist of a bridge rectifier off the 24V tap connected to a suitable filter cap of say 1000UF. This filtered DC will then be connected to a small surplus 12V regulator board and heat sink assembly which by the looks of it can handle 5A or better. I plan on mounting this regulator in the cabinet and providing a terminal strip for the 12V output. The DC load will probably never exceed .500 - .750 A. Now here is the dilemma. I haven't tried to put all this together yet, but I know that once I rectify and filter the 24VAC I'll probably end up with something like 30VDC out. The regulator uses a ua723, a TO3 and a smaller TO transistor as well a whole bunch of discrete components. I have no specs on this regulator, but it is well built, appears to be commercial grade, and although it might handle it fine I'd feel a lot better hitting it with something like 18VDC instead of 30. I would hate to blow it up trying to see if it would work on the higher input. I could add some series resistance either before or after the bridge, but the voltage drop across this resistance would vary depending on the total load and I'm not sure how well such a scheme would work. So I was thinking about employing a voltage divider at the output of the filter. The resistance ratio would be easy to figure out, however I'm just not sure how to determine the optimum resistor values. Does this seem like a viable plan, or perhaps someone my have other thoughts as to how to address this? If someone could please help me with this I would be very grateful. Thanks, Lenny Not clear exactly what you're doing, but the devil is in the details. Depending on the line voltage and the design of the transformer, but the unloaded voltage of the transformer may result significantly higher than 30V. The word "24V tap" begs the question of how the transformer is configured to get the 30VDC. You really need to characterize the 12V board. It doesn't take a "whole bunch" of discretes to make a 723 supply. There may be other things going on. You don't know what input min/max it can tolerate. You're gonna have a wide range in input voltage depending on line voltage and load current. And a couple of volts of ripple. Once you figure out how much headroom you have, insert a zener in the power input. You can make one from a small zener and a power transistor. Doesn't have to be all that accurate. And there are a lot of potential gotchas using an unknown board. For example, I build supplies that sense output current in the negative lead. They run from floating transformer windings. If I were to try to use the AC for some other purpose, stuffing current into my floating winding relative to ground would make a real mess of things. Making a dual-purpose power supply where both purposes are known is much easier than building an dual-output supply where none of the "purposes" are known in advance. |
#3
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Power supply question
On Mon, 18 Feb 2013 09:49:18 -0800 (PST), klem kedidelhopper
wrote: I'm in the process of building a dual purpose power supply. The supply will have two outputs. One will be 24VAC rated at 4.0 A. The load on this supply will probably never exceed 2.0 A. The second supply will consist of a bridge rectifier off the 24V tap connected to a suitable filter cap of say 1000UF. This filtered DC will then be connected to a small surplus 12V regulator board and heat sink assembly which by the looks of it can handle 5A or better. I plan on mounting this regulator in the cabinet and providing a terminal strip for the 12V output. The DC load will probably never exceed .500 - .750 A. Now here is the dilemma. I haven't tried to put all this together yet, but I know that once I rectify and filter the 24VAC I'll probably end up with something like 30VDC out. The regulator uses a ua723, a TO3 and a smaller TO transistor as well a whole bunch of discrete components. I have no specs on this regulator, but it is well built, appears to be commercial grade, and although it might handle it fine I'd feel a lot better hitting it with something like 18VDC instead of 30. I would hate to blow it up trying to see if it would work on the higher input. I could add some series resistance either before or after the bridge, but the voltage drop across this resistance would vary depending on the total load and I'm not sure how well such a scheme would work. So I was thinking about employing a voltage divider at the output of the filter. The resistance ratio would be easy to figure out, however I'm just not sure how to determine the optimum resistor values. Does this seem like a viable plan, or perhaps someone my have other thoughts as to how to address this? If someone could please help me with this I would be very grateful. Thanks, Lenny The best aproach would be to use a transformer with both 12V and 24V windings. Feeding 24VAC into a bridge rectifier will give you about 32 - 36 volts, depending on load. Using a rough approximation, your regulator would be dissipating 15 watts. I'd also boost the value of the main filter cap by at least a value of 10. An alternative approach may be to use a 7812 series regulator as an adjustable regulator. By using a voltage divider between the output, the reference (ground) pin, and true ground you could have an intermediate 18V regulated output to feed to your regulator. Check the 7812 data sheets for voltage readings and how to do this. If you have a variable power supply, or a variable transformer it may be possible to evaluate your regulator. Use a 100 ohm resistor between the power supply and the input pin of the regulator. Measure the voltage across the resistor while slowly increasing the voltage into the regulator. If a slight increase in input voltage results in a signiificant increase in voltage across the 100 ohm resistor you are above the maximum input voltage for the regulator. PlainBill |
#4
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Power supply question
klem kedidelhopper wrote:
I'm in the process of building a dual purpose power supply. The supply will have two outputs. One will be 24VAC rated at 4.0 A. The load on this supply will probably never exceed 2.0 A. The second supply will consist of a bridge rectifier off the 24V tap connected to a suitable filter cap of say 1000UF. This filtered DC will then be connected to a small surplus 12V regulator board and heat sink assembly which by the looks of it can handle 5A or better. I plan on mounting this regulator in the cabinet and providing a terminal strip for the 12V output. The DC load will probably never exceed .500 - .750 A. Now here is the dilemma. I haven't tried to put all this together yet, but I know that once I rectify and filter the 24VAC I'll probably end up with something like 30VDC out. The regulator uses a ua723, a TO3 and a smaller TO transistor as well a whole bunch of discrete components. I have no specs on this regulator, but it is well built, appears to be commercial grade, and although it might handle it fine I'd feel a lot better hitting it with something like 18VDC instead of 30. I would hate to blow it up trying to see if it would work on the higher input. I could add some series resistance either before or after the bridge, but the voltage drop across this resistance would vary depending on the total load and I'm not sure how well such a scheme would work. So I was thinking about employing a voltage divider at the output of the filter. The resistance ratio would be easy to figure out, however I'm just not sure how to determine the optimum resistor values. Does this seem like a viable plan, or perhaps someone my have other thoughts as to how to address this? If someone could please help me with this I would be very grateful. Thanks, Lenny It can handle up to 40volts on the input.. http://www.ti.com/lit/ds/symlink/lm723.pdf There is PDF with examples at the bottom for its use.. Jamie |
#5
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Power supply question
klem kedidelhopper wrote:
The second supply will consist of a bridge rectifier off the 24V tap connected to a suitable filter cap of say 1000UF. With a full-wave bridge rectifier, if you use an 8300 uF capacitor, the volts of ripple will equal the amps of load current. (Don Lancaster taught me this.) The proposed 1000 uF capacitor will have about 8 volts of ripple at a 1 amp load current. This is still above what the regulator probably needs as a minimum input, but you might want to consider a bigger capacitor. I could add some series resistance either before or after the bridge, but the voltage drop across this resistance would vary depending on the total load and I'm not sure how well such a scheme would work. I have a USB power supply that plugs in to the 12 V in my car that does this. The 12 V DC goes through a power resistor (around 5 W rating) and then into the input of a 7805 regulator in a TO-220 case. I'm not sure if they did this to move some of the heat dissipation from the regulator to the resistor, or just wanted to provide some current limiting for some failure modes of the regulator, or what. I've never put a meter on it but it seems to work OK. (The USB socket provides 5 V DC at 0.5 A, or 2.5 W.) If you don't have any better specs on what the parts will do, I'd try it and see. Install the transformer, bridge rectifier, and capacitor, but leave out the regulator. Load the 24 VAC output to 4 A. (If you don't have some power resistors sitting around, car tail light bulbs in series are good for this and you probably already own some.) Load the output of the bridge rectifier to 1 A. Plug the transformer in to the lowest line voltage you expect it to work at (use a Variac if you have one). Measure the DC at the output of the rectifier - that is the lowest DC input to the regulator you can expect. If you want, you can then disconnect the load on the 24 VAC output and on the rectifier, plug into the highest line voltage you expect (Variac again), and measure the DC again, to get the highest DC input to the regulator that you can expect. Then, you need to know the minimum DC input you can have to your regulator board for it to still regulate. If you already have a variable DC power supply, this is easy to figure out. If you don't, you have to guess; if it was a 7812 the standard answer is that you need about 13.5 to 14 V DC minimum for 12 V DC out. Your board may be designed for more than this, though. Once you know the lowest DC voltage you can expect from the rectifier, and the lowest DC voltage you can supply to the regulator, you can figure out how many volts maximum you have to drop in the resistor. Just on paper, if I guesstimate a minimum DC input to the regulator of 14 V, and a 1 A load, I have... Peak secondary voltage 24 V * 1.414 = 33.9 V Minus two diode drops 33.9 V - 2 V = 31.9 V Ripple with 1000 uF @ 1 A 31.9 V - 8 V = 23.9 V Minus regulator minimum 23.9 V - 14 V = 9.9 V Resistor needed 9.9 V / 1 A = 9.9 ohms 9.9 V * 1 A = 9.9 watts I would probably then look for something like an 8 ohm, 15 watt or better resistor. In perfect conditions, this would provide a little more DC to the input of the regulator, and in the real world, it would also account for getting less than 24 V DC from the transformer, slightly more diode drop, slightly worse ripple, etc. So I was thinking about employing a voltage divider at the output of the filter. The series resistor *is* a voltage divider. The regulator is the bottom resistor in the divider. Matt Roberds |
#6
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Power supply question
"klem kedidelhopper" wrote in message ... I'm in the process of building a dual purpose power supply. The supply will have two outputs. One will be 24VAC rated at 4.0 A. The load on this supply will probably never exceed 2.0 A. The second supply will consist of a bridge rectifier off the 24V tap connected to a suitable filter cap of say 1000UF. This filtered DC will then be connected to a small surplus 12V regulator board and heat sink assembly which by the looks of it can handle 5A or better. I plan on mounting this regulator in the cabinet and providing a terminal strip for the 12V output. The DC load will probably never exceed .500 - .750 A. Now here is the dilemma. I haven't tried to put all this together yet, but I know that once I rectify and filter the 24VAC I'll probably end up with something like 30VDC out. The regulator uses a ua723, a TO3 and a smaller TO transistor as well a whole bunch of discrete components. I have no specs on this regulator, but it is well built, appears to be commercial grade, and although it might handle it fine I'd feel a lot better hitting it with something like 18VDC instead of 30. I would hate to blow it up trying to see if it would work on the higher input. I could add some series resistance either before or after the bridge, but the voltage drop across this resistance would vary depending on the total load and I'm not sure how well such a scheme would work. So I was thinking about employing a voltage divider at the output of the filter. The resistance ratio would be easy to figure out, however I'm just not sure how to determine the optimum resistor values. Does this seem like a viable plan, or perhaps someone my have other thoughts as to how to address this? If someone could please help me with this I would be very grateful. Thanks, Lenny There's a good chance that there will be an electrolytic decoupling cap hung across the supply input of your regulator board. Might be anything from 10uF to 220uF. If you can find such a cap, look at it's voltage rating. If it's say 25v then the chances are that the board is not expecting more than 20v of input. If it's a 35v part, then probably 30v tops. You can drop a constant amount in a simple fashion by using a series zener rather than a series resistor, which would, as you surmise, produce a variable drop depending on load. You just put the zener in the line pointing 'backwards'. However, bear in mind that the power rating of the zener has to be sufficient, so if you were looking to drop say 10v at 0.5 A, you would be looking at a 5 watt minimum zener. As an alternative, 78xx regulators come in many voltages, including some quite high ones (I have 18s and 24s). Most will do at least an amp, and some versions more. Bear in mind if going down this route that you will need to heatsink the device, and you will need to add decoupling caps close to the pins to avoid instability problems. Arfa |
#7
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Power supply question
"klem kedidelhopper" Now here is the dilemma. I haven't tried to put all this together yet, but I know that once I rectify and filter the 24VAC I'll probably end up with something like 30VDC out. ** Likely about 35VDC unloaded I could add some series resistance either before or after the bridge, but the voltage drop across this resistance would vary depending on the total load and I'm not sure how well such a scheme would work. ** A string of say 20 x 3A diodes is the cheapest solution. Wired in series with the "+" terminal of the bridge, all mounted on a tag strip. Drops the DC level by about 12 to 15 volts, depending on the load. ..... Phil |
#8
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Power supply question
With a full-wave bridge rectifier, if you use an 8300 uF capacitor, the volts of ripple will equal the amps of load current. (Don Lancaster taught me this.) ** The correct value is 6300uF. Such a cap will drop 1 volt in 6.3mS, the typical discharge time in a full wave rectifier at 60Hz. For 50Hz full wave supplies, the value is 7500uF for 1V ripple at 1 amp. ..... Phil |
#9
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Power supply question
On Feb 19, 12:51*am, "Phil Allison" wrote:
With a full-wave bridge rectifier, if you use an 8300 uF capacitor, the volts of ripple will equal the amps of load current. *(Don Lancaster taught me this.) ** The correct value is 6300uF. Such a cap will drop 1 volt in 6.3mS, the typical discharge time in a full wave rectifier at 60Hz. For 50Hz full wave supplies, the value is 7500uF for 1V ripple at 1 amp. .... *Phil This is some great advice. Thank you everyone for all your input. I especially like the diode and Zener ideas. They/re cheap and should work well. I've got lots of diodes around here and I'm going to experiment with them. However after all this I remembered that the transformer is center tapped! At the time, I simply wire nutted the tap, tucked it down under the transformer and forgot about it. How this simple fact and the possibilities it presents slipped my mind is anyone's guess. I've been building this thing in the evenings after my usual work and perhaps I've been tired. The transformer measures 25.2V at 120V line unloaded. Loading the transformer in this fashion will probably unbalance it somewhat and drop the 24V a bit as well but I don't see it as a real problem. I should be able to use one side of the secondary and the tap now get at least 15 -17 VDC out of the bridge and filter, and that will provide a healthier input to my regulator. Lenny |
#10
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Power supply question
On 2/19/2013 5:01 PM, klem kedidelhopper wrote:
On Feb 19, 12:51 am, "Phil Allison" wrote: With a full-wave bridge rectifier, if you use an 8300 uF capacitor, the volts of ripple will equal the amps of load current. (Don Lancaster taught me this.) ** The correct value is 6300uF. Such a cap will drop 1 volt in 6.3mS, the typical discharge time in a full wave rectifier at 60Hz. For 50Hz full wave supplies, the value is 7500uF for 1V ripple at 1 amp. .... Phil This is some great advice. Thank you everyone for all your input. I especially like the diode and Zener ideas. They/re cheap and should work well. I've got lots of diodes around here and I'm going to experiment with them. However after all this I remembered that the transformer is center tapped! At the time, I simply wire nutted the tap, tucked it down under the transformer and forgot about it. How this simple fact and the possibilities it presents slipped my mind is anyone's guess. I've been building this thing in the evenings after my usual work and perhaps I've been tired. The transformer measures 25.2V at 120V line unloaded. Loading the transformer in this fashion will probably unbalance it somewhat and drop the 24V a bit as well but I don't see it as a real problem. I should be able to use one side of the secondary and the tap now get at least 15 -17 VDC out of the bridge and filter, and that will provide a healthier input to my regulator. Lenny No need to unbalance the transformer, just use 2 diodes and use the center tap as negative. See Here, http://metroamp.com/wiki/index.php/F..._Tap_Rectifier Mikek |
#11
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Power supply question
On Feb 20, 6:06*pm, amdx wrote:
On 2/19/2013 5:01 PM, klem kedidelhopper wrote: On Feb 19, 12:51 am, "Phil Allison" wrote: With a full-wave bridge rectifier, if you use an 8300 uF capacitor, the volts of ripple will equal the amps of load current. *(Don Lancaster taught me this.) ** The correct value is 6300uF. Such a cap will drop 1 volt in 6.3mS, the typical discharge time in a full wave rectifier at 60Hz. For 50Hz full wave supplies, the value is 7500uF for 1V ripple at 1 amp. .... *Phil This is some great advice. Thank you everyone for all your input. I especially like the diode and Zener ideas. They/re cheap and should work well. I've got lots of diodes around here and I'm going to experiment with them. However after all this I remembered that the transformer is center tapped! *At the time, I simply wire nutted the tap, tucked it down under the transformer and forgot about it. How this simple fact and the possibilities it presents slipped my mind is anyone's guess. I've been building this thing in the evenings after my usual work and perhaps I've been tired. The transformer measures 25.2V at 120V line unloaded. Loading the transformer in this fashion will probably unbalance it somewhat and drop the 24V a bit as well but I don't see it as a real problem. I should be able to use one side of the secondary and the tap now get at least 15 -17 VDC out of the bridge and filter, and that will provide a healthier input to my regulator. Lenny * *No need to unbalance the transformer, just use 2 diodes and use the center tap as negative. See Here, *http://metroamp.com/wiki/index.php/F..._Tap_Rectifier * * * * * * * * * * * * * * * * Mikek But won't that still give me 36VDC into my regulator? Lenny |
#12
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Power supply question
"klem kedidelhopper" No need to unbalance the transformer, just use 2 diodes and use the center tap as negative. See Here, http://metroamp.com/wiki/index.php/F..._Tap_Rectifier Mikek But won't that still give me 36VDC into my regulator? Lenny ** Nooooooh !! Get a ****ing brain. .... Phil |
#13
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Power supply question
"klem kedidelhopper" wrote in message ... On Feb 20, 6:06 pm, amdx wrote: On 2/19/2013 5:01 PM, klem kedidelhopper wrote: On Feb 19, 12:51 am, "Phil Allison" wrote: With a full-wave bridge rectifier, if you use an 8300 uF capacitor, the volts of ripple will equal the amps of load current. (Don Lancaster taught me this.) ** The correct value is 6300uF. Such a cap will drop 1 volt in 6.3mS, the typical discharge time in a full wave rectifier at 60Hz. For 50Hz full wave supplies, the value is 7500uF for 1V ripple at 1 amp. .... Phil This is some great advice. Thank you everyone for all your input. I especially like the diode and Zener ideas. They/re cheap and should work well. I've got lots of diodes around here and I'm going to experiment with them. However after all this I remembered that the transformer is center tapped! At the time, I simply wire nutted the tap, tucked it down under the transformer and forgot about it. How this simple fact and the possibilities it presents slipped my mind is anyone's guess. I've been building this thing in the evenings after my usual work and perhaps I've been tired. The transformer measures 25.2V at 120V line unloaded. Loading the transformer in this fashion will probably unbalance it somewhat and drop the 24V a bit as well but I don't see it as a real problem. I should be able to use one side of the secondary and the tap now get at least 15 -17 VDC out of the bridge and filter, and that will provide a healthier input to my regulator. Lenny No need to unbalance the transformer, just use 2 diodes and use the center tap as negative. See Here, http://metroamp.com/wiki/index.php/F..._Tap_Rectifier Mikek But won't that still give me 36VDC into my regulator? Lenny No, it won't Arfa |
#14
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Power supply question
On Sunday, February 24, 2013 10:17:29 AM UTC-5, Arfa Daily wrote:
"klem kedidelhopper" wrote in message ... On Feb 20, 6:06 pm, amdx wrote: On 2/19/2013 5:01 PM, klem kedidelhopper wrote: On Feb 19, 12:51 am, "Phil Allison" wrote: With a full-wave bridge rectifier, if you use an 8300 uF capacitor, the volts of ripple will equal the amps of load current. (Don Lancaster taught me this.) ** The correct value is 6300uF. Such a cap will drop 1 volt in 6.3mS, the typical discharge time in a full wave rectifier at 60Hz. For 50Hz full wave supplies, the value is 7500uF for 1V ripple at 1 amp. .... Phil This is some great advice. Thank you everyone for all your input. I especially like the diode and Zener ideas. They/re cheap and should work well. I've got lots of diodes around here and I'm going to experiment with them. However after all this I remembered that the transformer is center tapped! At the time, I simply wire nutted the tap, tucked it down under the transformer and forgot about it. How this simple fact and the possibilities it presents slipped my mind is anyone's guess. I've been building this thing in the evenings after my usual work and perhaps I've been tired. The transformer measures 25.2V at 120V line unloaded. Loading the transformer in this fashion will probably unbalance it somewhat and drop the 24V a bit as well but I don't see it as a real problem. I should be able to use one side of the secondary and the tap now get at least 15 -17 VDC out of the bridge and filter, and that will provide a healthier input to my regulator. Lenny No need to unbalance the transformer, just use 2 diodes and use the center tap as negative. See Here, http://metroamp.com/wiki/index.php/F..._Tap_Rectifier Mikek But won't that still give me 36VDC into my regulator? Lenny No, it won't Arfa I looked over what I had previously written and perhaps I didn’t explain this properly. I have a 24VCT transformer. The transformer needs to power 24VAC equipment as well as 12VDC equipment. For the DC circuit I first tried using a bridge directly off the 24V winding. As soon as I connected up the filter cap the DC output went to 35V, which is probably too high to feed my 12V regulator. Several people came up with some great ideas to address this, and I then realized that I had a center tap that was not being used. So I connected my bridge across the center tap and one side of the secondary. This time the 13VAC when FW rectified using the bridge went to about 19VDC, which is a safe input to the regulator. Although this worked, I wasn’t happy about unbalancing the transformer this way so I posted my results. Unless I seriously misunderstood It was suggested here that I come off the full secondary output with two diodes, cathodes tied together, (typical FW rectifier), and use the center tap as my negative return. I didn't think that would make any difference in the output voltage from using a bridge without the center tap however I tried it anyway. As I suspected it would, the DC output again went to 35V when I connected the filter up. I've been playing with power supplies all my life and maybe my age is catching up with me. I guess I just don't understand the explanation of how to get a lower voltage to my DC regulator by what I thought sounded like just configuring the transformer properly. So at the risk of sounding like a complete idiot here can someone please explain this further? Thanks, Lenny |
#16
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Power supply question
I looked over what I had previously written and perhaps I didn’t explain this properly. I have a 24VCT transformer. The transformer needs to power 24VAC equipment as well as 12VDC equipment. For the DC circuit I first tried using a bridge directly off the 24V winding. As soon as I connected up the filter cap the DC output went to 35V, which is probably too high to feed my 12V regulator. Several people came up with some great ideas to address this, and I then realized that I had a center tap that was not being used. So I connected my bridge across the center tap and one side of the secondary. This time the 13VAC when FW rectified using the bridge went to about 19VDC, which is a safe input to the regulator. Although this worked, I wasn’t happy about unbalancing the transformer this way so I posted my results. Unless I seriously misunderstood It was suggested here that I come off the full secondary output with two diodes, cathodes tied together, (typical FW rectifier), and use the center tap as my negative return. I didn't think that would make any difference in the output voltage from using a bridge without the center tap however I tried it anyway. As I suspected it would, the DC output again went to 35V when I connected the filter up. I've been playing with power supplies all my life and maybe my age is catching up with me. I guess I just don't understand the explanation of how to get a lower voltage to my DC regulator by what I thought sounded like just configuring the transformer properly. So at the risk of sounding like a complete idiot here can someone please explain this further? Thanks, Lenny OK. A bit clearer now. What you were originally proposing now seems OK provided that the 24v AC circuit is completely floating with respect to anything that you want to do at 12v - ie driving your regulator input - and the current that your 12v circuit is going to draw, is not a lot compared to the rating of the transformer, and the current that the AC circuit is going to draw is not near to the transformer's rating, then you should get away with running in the proposed 'unbalanced' way. I have done such things over the years, and gotten away with it. Although it's not very good practice, transformers are pretty forgiving components. I guess that the simple answer is try it, and see what happens ? Arfa |
#17
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Power supply question
On Feb 26, 5:16*am, "Arfa Daily" wrote:
I looked over what I had previously written and perhaps I didn’t explain this properly. I have a 24VCT transformer. The transformer needs to power 24VAC equipment as well as 12VDC equipment. For the DC circuit I first tried using a bridge directly off the 24V winding. As soon as I connected up the filter cap the DC output went to 35V, which is probably too high to feed my 12V regulator. Several people came up with some great ideas to address this, and I then realized that I had a center tap that was not being used. So I connected my bridge across the center tap and one side of the secondary. This time the 13VAC when FW rectified using the bridge went to about 19VDC, which is a safe input to the regulator. Although this worked, I wasn’t happy about unbalancing the transformer this way so I posted my results. Unless I seriously misunderstood It was suggested here that I come off the full secondary output with two diodes, cathodes tied together, (typical FW rectifier), and use the center tap as my negative return. I didn't think that would make any difference in the output voltage from using a bridge without the center tap however I tried it anyway. As I suspected it would, the DC output again went to 35V when I connected the filter up. I've been playing with power supplies all my life and maybe my age is catching up with me. I guess I just don't understand the explanation of how to get a lower voltage to my DC regulator by what I thought sounded like just configuring the transformer properly. So at the risk of sounding like a complete idiot here can someone please explain this further? Thanks, Lenny OK. A bit clearer now. What you were originally proposing now seems OK provided that the 24v AC circuit is completely floating with respect to anything that you want to do at 12v - ie driving your regulator input - and the current that your 12v circuit is going to draw, is not a lot compared to the rating of the transformer, and the current that the AC circuit is going to draw is not near to the transformer's rating, then you should get away with running in the proposed 'unbalanced' way. I have done such things over the years, and gotten away with it. Although it's not very good practice, transformers are pretty forgiving components. I guess that the simple answer is try it, and see what happens ? Arfa I'm grateful for everyone's input, and although this power supply as well as the equipment that it will power is to be used in a family business, never the less I'm trying to build this as "technically correct" as possible. I found some 6.8V 10W stud mount zeners in the junk box last night. I'm thinking that they may be a bit light for this but I might try stringing two or possibly three of them together on a heat sink as Arfa suggested or perhaps try the series diode trick, (from Phil), both as previously mentioned on the output of the filter and see what happens. Even though given the load it may work fine it would be nice as Arfa said to not have to "unbalance the transformer. Lenny |
#18
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Power supply question
"klem kedidelhopper" wrote in message ... On Feb 26, 5:16 am, "Arfa Daily" wrote: I looked over what I had previously written and perhaps I didn’t explain this properly. I have a 24VCT transformer. The transformer needs to power 24VAC equipment as well as 12VDC equipment. For the DC circuit I first tried using a bridge directly off the 24V winding. As soon as I connected up the filter cap the DC output went to 35V, which is probably too high to feed my 12V regulator. Several people came up with some great ideas to address this, and I then realized that I had a center tap that was not being used. So I connected my bridge across the center tap and one side of the secondary. This time the 13VAC when FW rectified using the bridge went to about 19VDC, which is a safe input to the regulator. Although this worked, I wasn’t happy about unbalancing the transformer this way so I posted my results. Unless I seriously misunderstood It was suggested here that I come off the full secondary output with two diodes, cathodes tied together, (typical FW rectifier), and use the center tap as my negative return. I didn't think that would make any difference in the output voltage from using a bridge without the center tap however I tried it anyway. As I suspected it would, the DC output again went to 35V when I connected the filter up. I've been playing with power supplies all my life and maybe my age is catching up with me. I guess I just don't understand the explanation of how to get a lower voltage to my DC regulator by what I thought sounded like just configuring the transformer properly. So at the risk of sounding like a complete idiot here can someone please explain this further? Thanks, Lenny OK. A bit clearer now. What you were originally proposing now seems OK provided that the 24v AC circuit is completely floating with respect to anything that you want to do at 12v - ie driving your regulator input - and the current that your 12v circuit is going to draw, is not a lot compared to the rating of the transformer, and the current that the AC circuit is going to draw is not near to the transformer's rating, then you should get away with running in the proposed 'unbalanced' way. I have done such things over the years, and gotten away with it. Although it's not very good practice, transformers are pretty forgiving components. I guess that the simple answer is try it, and see what happens ? Arfa I'm grateful for everyone's input, and although this power supply as well as the equipment that it will power is to be used in a family business, never the less I'm trying to build this as "technically correct" as possible. I found some 6.8V 10W stud mount zeners in the junk box last night. I'm thinking that they may be a bit light for this but I might try stringing two or possibly three of them together on a heat sink as Arfa suggested or perhaps try the series diode trick, (from Phil), both as previously mentioned on the output of the filter and see what happens. Even though given the load it may work fine it would be nice as Arfa said to not have to "unbalance the transformer. Lenny That would make the zeners good for about an amp and a half tops. Bear in mind that in order to string them in series on a heatsink, the studs will need to be insulated from it. These stud mount diodes often come with insulating mounting hardware. I think as an initial try-out, I'd just put one in the line and see what you get. Should knock you down to something just above 28 v from your 35 v starting point. Let us know how you get on Arfa |
#20
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Power supply question
On Feb 26, 6:39*pm, Jamie
t wrote: wrote: On Sunday, February 24, 2013 10:17:29 AM UTC-5, Arfa Daily wrote: "klem kedidelhopper" wrote in message ... On Feb 20, 6:06 pm, amdx wrote: On 2/19/2013 5:01 PM, klem kedidelhopper wrote: On Feb 19, 12:51 am, "Phil Allison" wrote: With a full-wave bridge rectifier, if you use an 8300 uF capacitor, the volts of ripple will equal the amps of load current. *(Don Lancaster taught me this.) ** The correct value is 6300uF. Such a cap will drop 1 volt in 6.3mS, the typical discharge time in a full wave rectifier at 60Hz. For 50Hz full wave supplies, the value is 7500uF for 1V ripple at 1 amp. .... *Phil This is some great advice. Thank you everyone for all your input. I especially like the diode and Zener ideas. They/re cheap and should work well. I've got lots of diodes around here and I'm going to experiment with them. However after all this I remembered that the transformer is center tapped! *At the time, I simply wire nutted the tap, tucked it down under the transformer and forgot about it. How this simple fact and the possibilities it presents slipped my mind is anyone's guess. I've been building this thing in the evenings after my usual work and perhaps I've been tired. The transformer measures 25.2V at 120V line unloaded. Loading the transformer in this fashion will probably unbalance it somewhat and drop the 24V a bit as well but I don't see it as a real problem. I should be able to use one side of the secondary and the tap now get at least 15 -17 VDC out of the bridge and filter, and that will provide a healthier input to my regulator. Lenny * No need to unbalance the transformer, just use 2 diodes and use the center tap as negative. See Here, http://metroamp.com/wiki/index.php/F..._Tap_Rectifier * * * * * * * * * * * * * * * *Mikek But won't that still give me 36VDC into my regulator? Lenny No, it won't Arfa I looked over what I had previously written and perhaps I didn’t explain this properly. I have a 24VCT transformer. The transformer needs to power 24VAC equipment as well as 12VDC equipment. For the DC circuit I first tried using a bridge directly off the 24V winding. As soon as I connected up the filter cap the DC output went to 35V, which is probably too high to feed my 12V regulator. Several people came up with some great ideas to address this, and I then realized that I had a center tap that was not being used. So I connected my bridge across the center tap and one side of the secondary. This time the 13VAC when FW rectified using the bridge went to about 19VDC, which is *a safe input to the regulator. Although this worked, I wasn’t happy about unbalancing the transformer this way so I posted my results. Unless I seriously misunderstood It was suggested here that I come off the full secondary output with two diodes, cathodes tied together, (typical FW rectifier), and use the center tap as my negative return. I didn't think that would make any difference in the output voltage from using a bridge without the center tap however I tried it anyway. As I suspected it would, the DC output again went to 35V when I connected the filter up. I've been playing with power supplies all my life and maybe my age is catching up with me. I guess I just don't understand the explanation of how to get a lower voltage to my DC regulator by what I thought sounded like just configuring the transformer properly. So at the risk of sounding like a complete idiot here can someone please explain this further? Thanks, Lenny * Your problem is simple * *If the 24V AC devices does not come in contact with the common or ground of this supply you have, you can use a 2 diode full wave config. * *The center tap would be your common for the 12 volt supply, one diode from each outter leg joined together to form a full wave. The diode output alogn with using the center tap as your common will give you 12 * 1.414 volts unloaded. If you need to use a 12 Volt reg, I guess you could do that. Use a LDO type. * As for the 24 v AC, the outter legs will supply that to the out board device. Make sure the AC legs do not come in contact with either grd or DC out.. * * * * * * * * * * * * * * * * * o * * * *o * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * * | * * * * | to your 24V AC device * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * + * * * * * * * * * | * * * * | * * * * * * * *--------------+. ,-o---------|-----|-+--+ * * * * * * * * * * * * * * * )|( * * * * * | * * * * * | * *18DC * * * * * * * * * * * * * * * )|( * * * * * | * * * * * +------++ * * * * *Line Voltage * * * *-. ,-+----+| * | * * * * * | * * === * * * * * * * * * * * * * * * )|( * * *=== *| * * * * * | * * /-\ * * * * * * * * * * * * * * * )|( * * *GND *| * * * * * | * * *| * * * * * * * +-------------+-' '+----------o-----|+----+ * *=== * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * GND (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) * Unless I missed something, I don't see a problem? Jamie |
#21
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Power supply question
On Feb 26, 6:39*pm, Jamie
t wrote: wrote: On Sunday, February 24, 2013 10:17:29 AM UTC-5, Arfa Daily wrote: "klem kedidelhopper" wrote in message ... On Feb 20, 6:06 pm, amdx wrote: On 2/19/2013 5:01 PM, klem kedidelhopper wrote: On Feb 19, 12:51 am, "Phil Allison" wrote: With a full-wave bridge rectifier, if you use an 8300 uF capacitor, the volts of ripple will equal the amps of load current. *(Don Lancaster taught me this.) ** The correct value is 6300uF. Such a cap will drop 1 volt in 6.3mS, the typical discharge time in a full wave rectifier at 60Hz. For 50Hz full wave supplies, the value is 7500uF for 1V ripple at 1 amp. .... *Phil This is some great advice. Thank you everyone for all your input. I especially like the diode and Zener ideas. They/re cheap and should work well. I've got lots of diodes around here and I'm going to experiment with them. However after all this I remembered that the transformer is center tapped! *At the time, I simply wire nutted the tap, tucked it down under the transformer and forgot about it. How this simple fact and the possibilities it presents slipped my mind is anyone's guess. I've been building this thing in the evenings after my usual work and perhaps I've been tired. The transformer measures 25.2V at 120V line unloaded. Loading the transformer in this fashion will probably unbalance it somewhat and drop the 24V a bit as well but I don't see it as a real problem. I should be able to use one side of the secondary and the tap now get at least 15 -17 VDC out of the bridge and filter, and that will provide a healthier input to my regulator. Lenny * No need to unbalance the transformer, just use 2 diodes and use the center tap as negative. See Here, http://metroamp.com/wiki/index.php/F..._Tap_Rectifier * * * * * * * * * * * * * * * *Mikek But won't that still give me 36VDC into my regulator? Lenny No, it won't Arfa I looked over what I had previously written and perhaps I didn’t explain this properly. I have a 24VCT transformer. The transformer needs to power 24VAC equipment as well as 12VDC equipment. For the DC circuit I first tried using a bridge directly off the 24V winding. As soon as I connected up the filter cap the DC output went to 35V, which is probably too high to feed my 12V regulator. Several people came up with some great ideas to address this, and I then realized that I had a center tap that was not being used. So I connected my bridge across the center tap and one side of the secondary. This time the 13VAC when FW rectified using the bridge went to about 19VDC, which is *a safe input to the regulator. Although this worked, I wasn’t happy about unbalancing the transformer this way so I posted my results. Unless I seriously misunderstood It was suggested here that I come off the full secondary output with two diodes, cathodes tied together, (typical FW rectifier), and use the center tap as my negative return. I didn't think that would make any difference in the output voltage from using a bridge without the center tap however I tried it anyway. As I suspected it would, the DC output again went to 35V when I connected the filter up. I've been playing with power supplies all my life and maybe my age is catching up with me. I guess I just don't understand the explanation of how to get a lower voltage to my DC regulator by what I thought sounded like just configuring the transformer properly. So at the risk of sounding like a complete idiot here can someone please explain this further? Thanks, Lenny * Your problem is simple * *If the 24V AC devices does not come in contact with the common or ground of this supply you have, you can use a 2 diode full wave config. * *The center tap would be your common for the 12 volt supply, one diode from each outter leg joined together to form a full wave. The diode output alogn with using the center tap as your common will give you 12 * 1.414 volts unloaded. If you need to use a 12 Volt reg, I guess you could do that. Use a LDO type. * As for the 24 v AC, the outter legs will supply that to the out board device. Make sure the AC legs do not come in contact with either grd or DC out.. * * * * * * * * * * * * * * * * * o * * * *o * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * * | * * * * | to your 24V AC device * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * + * * * * * * * * * | * * * * | * * * * * * * *--------------+. ,-o---------|-----|-+--+ * * * * * * * * * * * * * * * )|( * * * * * | * * * * * | * *18DC * * * * * * * * * * * * * * * )|( * * * * * | * * * * * +------++ * * * * *Line Voltage * * * *-. ,-+----+| * | * * * * * | * * === * * * * * * * * * * * * * * * )|( * * *=== *| * * * * * | * * /-\ * * * * * * * * * * * * * * * )|( * * *GND *| * * * * * | * * *| * * * * * * * +-------------+-' '+----------o-----|+----+ * *=== * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * GND (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) * Unless I missed something, I don't see a problem? Jamie I know it's difficult when we're only using text but I just can't understand, (read that is) your schematic. From your description though it sounds like it might be the FW arrangement I've already tried and got 35V out of. Is there any way to make that appear any more readable? Lenny |
#22
Posted to sci.electronics.repair
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Power supply question
On Feb 26, 6:39*pm, Jamie
t wrote: wrote: On Sunday, February 24, 2013 10:17:29 AM UTC-5, Arfa Daily wrote: "klem kedidelhopper" wrote in message ... On Feb 20, 6:06 pm, amdx wrote: On 2/19/2013 5:01 PM, klem kedidelhopper wrote: On Feb 19, 12:51 am, "Phil Allison" wrote: With a full-wave bridge rectifier, if you use an 8300 uF capacitor, the volts of ripple will equal the amps of load current. *(Don Lancaster taught me this.) ** The correct value is 6300uF. Such a cap will drop 1 volt in 6.3mS, the typical discharge time in a full wave rectifier at 60Hz. For 50Hz full wave supplies, the value is 7500uF for 1V ripple at 1 amp. .... *Phil This is some great advice. Thank you everyone for all your input. I especially like the diode and Zener ideas. They/re cheap and should work well. I've got lots of diodes around here and I'm going to experiment with them. However after all this I remembered that the transformer is center tapped! *At the time, I simply wire nutted the tap, tucked it down under the transformer and forgot about it. How this simple fact and the possibilities it presents slipped my mind is anyone's guess. I've been building this thing in the evenings after my usual work and perhaps I've been tired. The transformer measures 25.2V at 120V line unloaded. Loading the transformer in this fashion will probably unbalance it somewhat and drop the 24V a bit as well but I don't see it as a real problem. I should be able to use one side of the secondary and the tap now get at least 15 -17 VDC out of the bridge and filter, and that will provide a healthier input to my regulator. Lenny * No need to unbalance the transformer, just use 2 diodes and use the center tap as negative. See Here, http://metroamp.com/wiki/index.php/F..._Tap_Rectifier * * * * * * * * * * * * * * * *Mikek But won't that still give me 36VDC into my regulator? Lenny No, it won't Arfa I looked over what I had previously written and perhaps I didn’t explain this properly. I have a 24VCT transformer. The transformer needs to power 24VAC equipment as well as 12VDC equipment. For the DC circuit I first tried using a bridge directly off the 24V winding. As soon as I connected up the filter cap the DC output went to 35V, which is probably too high to feed my 12V regulator. Several people came up with some great ideas to address this, and I then realized that I had a center tap that was not being used. So I connected my bridge across the center tap and one side of the secondary. This time the 13VAC when FW rectified using the bridge went to about 19VDC, which is *a safe input to the regulator. Although this worked, I wasn’t happy about unbalancing the transformer this way so I posted my results. Unless I seriously misunderstood It was suggested here that I come off the full secondary output with two diodes, cathodes tied together, (typical FW rectifier), and use the center tap as my negative return. I didn't think that would make any difference in the output voltage from using a bridge without the center tap however I tried it anyway. As I suspected it would, the DC output again went to 35V when I connected the filter up. I've been playing with power supplies all my life and maybe my age is catching up with me. I guess I just don't understand the explanation of how to get a lower voltage to my DC regulator by what I thought sounded like just configuring the transformer properly. So at the risk of sounding like a complete idiot here can someone please explain this further? Thanks, Lenny * Your problem is simple * *If the 24V AC devices does not come in contact with the common or ground of this supply you have, you can use a 2 diode full wave config. * *The center tap would be your common for the 12 volt supply, one diode from each outter leg joined together to form a full wave. The diode output alogn with using the center tap as your common will give you 12 * 1.414 volts unloaded. If you need to use a 12 Volt reg, I guess you could do that. Use a LDO type. * As for the 24 v AC, the outter legs will supply that to the out board device. Make sure the AC legs do not come in contact with either grd or DC out.. * * * * * * * * * * * * * * * * * o * * * *o * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * * | * * * * | to your 24V AC device * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * * | * * * * | * * * * * * * + * * * * * * * * * | * * * * | * * * * * * * *--------------+. ,-o---------|-----|-+--+ * * * * * * * * * * * * * * * )|( * * * * * | * * * * * | * *18DC * * * * * * * * * * * * * * * )|( * * * * * | * * * * * +------++ * * * * *Line Voltage * * * *-. ,-+----+| * | * * * * * | * * === * * * * * * * * * * * * * * * )|( * * *=== *| * * * * * | * * /-\ * * * * * * * * * * * * * * * )|( * * *GND *| * * * * * | * * *| * * * * * * * +-------------+-' '+----------o-----|+----+ * *=== * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * GND (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) * Unless I missed something, I don't see a problem? Jamie I'm not sure if my last reply worked so I'll try it again. I know that it's very difficult when all we can use here is text but I'm afraid that I just can't understand, (read) your schematic. From you description however it appears to be the FW arrangement that I've already tried and got 35 V out of after I connected up the filter. Is there any way to make your diagram any more readable in this medium? Thanks, Lenny |
#23
Posted to sci.electronics.repair
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Power supply question
klem kedidelhopper wrote: On Feb 26, 6:39 pm, Jamie t wrote: wrote: On Sunday, February 24, 2013 10:17:29 AM UTC-5, Arfa Daily wrote: "klem kedidelhopper" wrote in message ... On Feb 20, 6:06 pm, amdx wrote: On 2/19/2013 5:01 PM, klem kedidelhopper wrote: On Feb 19, 12:51 am, "Phil Allison" wrote: With a full-wave bridge rectifier, if you use an 8300 uF capacitor, the volts of ripple will equal the amps of load current. (Don Lancaster taught me this.) ** The correct value is 6300uF. Such a cap will drop 1 volt in 6.3mS, the typical discharge time in a full wave rectifier at 60Hz. For 50Hz full wave supplies, the value is 7500uF for 1V ripple at 1 amp. .... Phil This is some great advice. Thank you everyone for all your input. I especially like the diode and Zener ideas. They/re cheap and should work well. I've got lots of diodes around here and I'm going to experiment with them. However after all this I remembered that the transformer is center tapped! At the time, I simply wire nutted the tap, tucked it down under the transformer and forgot about it. How this simple fact and the possibilities it presents slipped my mind is anyone's guess. I've been building this thing in the evenings after my usual work and perhaps I've been tired. The transformer measures 25.2V at 120V line unloaded. Loading the transformer in this fashion will probably unbalance it somewhat and drop the 24V a bit as well but I don't see it as a real problem. I should be able to use one side of the secondary and the tap now get at least 15 -17 VDC out of the bridge and filter, and that will provide a healthier input to my regulator. Lenny No need to unbalance the transformer, just use 2 diodes and use the center tap as negative. See Here, http://metroamp.com/wiki/index.php/F..._Tap_Rectifier Mikek But won't that still give me 36VDC into my regulator? Lenny No, it won't Arfa I looked over what I had previously written and perhaps I didn’t explain this properly. I have a 24VCT transformer. The transformer needs to power 24VAC equipment as well as 12VDC equipment. For the DC circuit I first tried using a bridge directly off the 24V winding. As soon as I connected up the filter cap the DC output went to 35V, which is probably too high to feed my 12V regulator. Several people came up with some great ideas to address this, and I then realized that I had a center tap that was not being used. So I connected my bridge across the center tap and one side of the secondary. This time the 13VAC when FW rectified using the bridge went to about 19VDC, which is a safe input to the regulator. Although this worked, I wasn’t happy about unbalancing the transformer this way so I posted my results. Unless I seriously misunderstood It was suggested here that I come off the full secondary output with two diodes, cathodes tied together, (typical FW rectifier), and use the center tap as my negative return. I didn't think that would make any difference in the output voltage from using a bridge without the center tap however I tried it anyway. As I suspected it would, the DC output again went to 35V when I connected the filter up. I've been playing with power supplies all my life and maybe my age is catching up with me. I guess I just don't understand the explanation of how to get a lower voltage to my DC regulator by what I thought sounded like just configuring the transformer properly. So at the risk of sounding like a complete idiot here can someone please explain this further? Thanks, Lenny Your problem is simple If the 24V AC devices does not come in contact with the common or ground of this supply you have, you can use a 2 diode full wave config. The center tap would be your common for the 12 volt supply, one diode from each outter leg joined together to form a full wave. The diode output alogn with using the center tap as your common will give you 12 * 1.414 volts unloaded. If you need to use a 12 Volt reg, I guess you could do that. Use a LDO type. As for the 24 v AC, the outter legs will supply that to the out board device. Make sure the AC legs do not come in contact with either grd or DC out.. o o | | | | to your 24V AC device | | | | | | | | | | | | + | | --------------+. ,-o---------|-----|-+--+ )|( | | 18DC )|( | +------++ Line Voltage -. ,-+----+| | | === )|( === | | /-\ )|( GND | | | +-------------+-' '+----------o-----|+----+ === GND (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) Unless I missed something, I don't see a problem? Jamie I'm not sure if my last reply worked so I'll try it again. I know that it's very difficult when all we can use here is text but I'm afraid that I just can't understand, (read) your schematic. From you description however it appears to be the FW arrangement that I've already tried and got 35 V out of after I connected up the filter. Is there any way to make your diagram any more readable in this medium? Thanks, Lenny Copy it and paste it into Wordpad, with the Courier New font. Google Groups uses a proportional font which screws up drawings. |
#24
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Power supply question
klem kedidelhopper wrote:
On Feb 26, 6:39 pm, Jamie t wrote: wrote: On Sunday, February 24, 2013 10:17:29 AM UTC-5, Arfa Daily wrote: "klem kedidelhopper" wrote in message ... On Feb 20, 6:06 pm, amdx wrote: On 2/19/2013 5:01 PM, klem kedidelhopper wrote: On Feb 19, 12:51 am, "Phil Allison" wrote: With a full-wave bridge rectifier, if you use an 8300 uF capacitor, the volts of ripple will equal the amps of load current. (Don Lancaster taught me this.) ** The correct value is 6300uF. Such a cap will drop 1 volt in 6.3mS, the typical discharge time in a full wave rectifier at 60Hz. For 50Hz full wave supplies, the value is 7500uF for 1V ripple at 1 amp. .... Phil This is some great advice. Thank you everyone for all your input. I especially like the diode and Zener ideas. They/re cheap and should work well. I've got lots of diodes around here and I'm going to experiment with them. However after all this I remembered that the transformer is center tapped! At the time, I simply wire nutted the tap, tucked it down under the transformer and forgot about it. How this simple fact and the possibilities it presents slipped my mind is anyone's guess. I've been building this thing in the evenings after my usual work and perhaps I've been tired. The transformer measures 25.2V at 120V line unloaded. Loading the transformer in this fashion will probably unbalance it somewhat and drop the 24V a bit as well but I don't see it as a real problem. I should be able to use one side of the secondary and the tap now get at least 15 -17 VDC out of the bridge and filter, and that will provide a healthier input to my regulator. Lenny No need to unbalance the transformer, just use 2 diodes and use the center tap as negative. See Here, http://metroamp.com/wiki/index.php/F..._Tap_Rectifier Mikek But won't that still give me 36VDC into my regulator? Lenny No, it won't Arfa I looked over what I had previously written and perhaps I didn’t explain this properly. I have a 24VCT transformer. The transformer needs to power 24VAC equipment as well as 12VDC equipment. For the DC circuit I first tried using a bridge directly off the 24V winding. As soon as I connected up the filter cap the DC output went to 35V, which is probably too high to feed my 12V regulator. Several people came up with some great ideas to address this, and I then realized that I had a center tap that was not being used. So I connected my bridge across the center tap and one side of the secondary. This time the 13VAC when FW rectified using the bridge went to about 19VDC, which is a safe input to the regulator. Although this worked, I wasn’t happy about unbalancing the transformer this way so I posted my results. Unless I seriously misunderstood It was suggested here that I come off the full secondary output with two diodes, cathodes tied together, (typical FW rectifier), and use the center tap as my negative return. I didn't think that would make any difference in the output voltage from using a bridge without the center tap however I tried it anyway. As I suspected it would, the DC output again went to 35V when I connected the filter up. I've been playing with power supplies all my life and maybe my age is catching up with me. I guess I just don't understand the explanation of how to get a lower voltage to my DC regulator by what I thought sounded like just configuring the transformer properly. So at the risk of sounding like a complete idiot here can someone please explain this further? Thanks, Lenny Your problem is simple If the 24V AC devices does not come in contact with the common or ground of this supply you have, you can use a 2 diode full wave config. The center tap would be your common for the 12 volt supply, one diode from each outter leg joined together to form a full wave. The diode output alogn with using the center tap as your common will give you 12 * 1.414 volts unloaded. If you need to use a 12 Volt reg, I guess you could do that. Use a LDO type. As for the 24 v AC, the outter legs will supply that to the out board device. Make sure the AC legs do not come in contact with either grd or DC out.. o o | | | | to your 24V AC device | | | | | | | | | | | | + | | --------------+. ,-o---------|-----|-+--+ )|( | | 18DC )|( | +------++ Line Voltage -. ,-+----+| | | === )|( === | | /-\ )|( GND | | | +-------------+-' '+----------o-----|+----+ === GND (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) Unless I missed something, I don't see a problem? Jamie I'm not sure if my last reply worked so I'll try it again. I know that it's very difficult when all we can use here is text but I'm afraid that I just can't understand, (read) your schematic. From you description however it appears to be the FW arrangement that I've already tried and got 35 V out of after I connected up the filter. Is there any way to make your diagram any more readable in this medium? Thanks, Lenny THe FW you tried was a 4 diode bridge, this is a 2 diode full wave config. THe difference being is, the CT (Center tap) is your common, the negative terminal and where the Cathode of the 2 diodes come together are the (+) terminal which will be around 18VDC with Cap attached If you truly do have a 24 volt transformer with CT, this means you'll get 12 Volts from each outer leg with respect to the CT. Because they are out of phase with each other (180), this is a split phase configuration, like seen in residential pole pigs in the USA. If you have done this and gotten 36 volts, then you actually have a 48V transformer with CT Jamie |
#25
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Power supply question
On Feb 27, 6:21*pm, Jamie
t wrote: klem kedidelhopper wrote: On Feb 26, 6:39 pm, Jamie t wrote: wrote: On Sunday, February 24, 2013 10:17:29 AM UTC-5, Arfa Daily wrote: "klem kedidelhopper" wrote in message .... On Feb 20, 6:06 pm, amdx wrote: On 2/19/2013 5:01 PM, klem kedidelhopper wrote: On Feb 19, 12:51 am, "Phil Allison" wrote: With a full-wave bridge rectifier, if you use an 8300 uF capacitor, the volts of ripple will equal the amps of load current. *(Don Lancaster taught me this.) ** The correct value is 6300uF. Such a cap will drop 1 volt in 6.3mS, the typical discharge time in a full wave rectifier at 60Hz. For 50Hz full wave supplies, the value is 7500uF for 1V ripple at 1 amp. .... *Phil This is some great advice. Thank you everyone for all your input. I especially like the diode and Zener ideas. They/re cheap and should work well. I've got lots of diodes around here and I'm going to experiment with them. However after all this I remembered that the transformer is center tapped! *At the time, I simply wire nutted the tap, tucked it down under the transformer and forgot about it. How this simple fact and the possibilities it presents slipped my mind is anyone's guess. I've been building this thing in the evenings after my usual work and perhaps I've been tired. The transformer measures 25.2V at 120V line unloaded. Loading the transformer in this fashion will probably unbalance it somewhat and drop the 24V a bit as well but I don't see it as a real problem. I should be able to use one side of the secondary and the tap now get at least 15 -17 VDC out of the bridge and filter, and that will provide a healthier input to my regulator. Lenny *No need to unbalance the transformer, just use 2 diodes and use the center tap as negative. See Here, http://metroamp.com/wiki/index.php/F..._Tap_Rectifier * * * * * * * * * * * * * * * Mikek But won't that still give me 36VDC into my regulator? Lenny No, it won't Arfa I looked over what I had previously written and perhaps I didn’t explain this properly. I have a 24VCT transformer. The transformer needs to power 24VAC equipment as well as 12VDC equipment. For the DC circuit I first tried using a bridge directly off the 24V winding. As soon as I connected up the filter cap the DC output went to 35V, which is probably too high to feed my 12V regulator. Several people came up with some great ideas to address this, and I then realized that I had a center tap that was not being used. So I connected my bridge across the center tap and one side of the secondary. This time the 13VAC when FW rectified using the bridge went to about 19VDC, which is *a safe input to the regulator. Although this worked, I wasn’t happy about unbalancing the transformer this way so I posted my results. Unless I seriously misunderstood It was suggested here that I come off the full secondary output with two diodes, cathodes tied together, (typical FW rectifier), and use the center tap as my negative return. I didn't think that would make any difference in the output voltage from using a bridge without the center tap however I tried it anyway. As I suspected it would, the DC output again went to 35V when I connected the filter up. I've been playing with power supplies all my life and maybe my age is catching up with me. I guess I just don't understand the explanation of how to get a lower voltage to my DC regulator by what I thought sounded like just configuring the transformer properly. So at the risk of sounding like a complete idiot here can someone please explain this further? Thanks, Lenny *Your problem is simple * If the 24V AC devices does not come in contact with the common or ground of this supply you have, you can use a 2 diode full wave config. * The center tap would be your common for the 12 volt supply, one diode from each outter leg joined together to form a full wave. The diode output alogn with using the center tap as your common will give you 12 * 1.414 volts unloaded. If you need to use a 12 Volt reg, I guess you could do that. Use a LDO type. *As for the 24 v AC, the outter legs will supply that to the out board device. Make sure the AC legs do not come in contact with either grd or DC out.. * * * * * * * * * * * * * * * * *o * * * *o * * * * * * * * * * * * * * * * *| * * * * | * * * * * * * * * * * * * * * * *| * * * * | to your 24V AC device * * * * * * * * * * * * * * * * *| * * * * | * * * * * * * * * * * * * * * * *| * * * * | * * * * * * * * * * * * * * * * *| * * * * | * * * * * * * * * * * * * * * * *| * * * * | * * * * * * * * * * * * * * * * *| * * * * | * * * * * * * * * * * * * * * * *| * * * * | * * * * * * *+ * * * * * * * * * | * * * * | * * * * * * * --------------+. ,-o---------|-----|-+--+ * * * * * * * * * * * * * * *)|( * * * * * | * * * * * | * *18DC * * * * * * * * * * * * * * *)|( * * * * * | * * * * * +------++ * * * * Line Voltage * * * *-. ,-+----+| * | * * * * * | * * === * * * * * * * * * * * * * * *)|( * * *=== *| * * * * * | * * /-\ * * * * * * * * * * * * * * *)|( * * *GND *| * * * * * | * * *| * * * * * * *+-------------+-' '+----------o-----|+----+ * *=== * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *GND (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) *Unless I missed something, I don't see a problem? Jamie I'm not sure if my last reply worked so I'll try it again. I know that it's very difficult when all we can use here is text but I'm afraid that I just can't understand, (read) your schematic. From you description however it appears to be the FW arrangement that I've already tried and got 35 V out of after I connected up the filter. Is there any way to make your diagram any more readable in this medium? Thanks, Lenny * THe FW you tried was a 4 diode bridge, this is a 2 diode full wave config. * *THe difference being is, the CT (Center tap) is your common, the negative terminal and where the Cathode of the 2 diodes come together are the (+) terminal which will be around 18VDC with Cap attached * If you truly do have a 24 volt transformer with CT, this means you'll get 12 Volts from each outer leg with respect to the CT. Because they are out of phase with each other (180), this is a split phase configuration, like seen in residential pole pigs in the USA. * If you have done this and gotten 36 volts, then you actually have a 48V transformer with CT Jamie What you're referring to is a 12VCT transformer. Connecting either a bridge and not using a center tap or just two diodes across the full secondary with cathodes tied together using CT as common connected to an output filter will yield 18VDC. A 24 V transformer under the same circumstances will produce 36VDC. I've tried it and it does. Lenny. |
#26
Posted to sci.electronics.repair
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Power supply question
"klem kedidelhopper" If you have done this and gotten 36 volts, then you actually have a 48V transformer with CT Jamie What you're referring to is a 12VCT transformer. Connecting either a bridge and not using a center tap or just two diodes across the full secondary with cathodes tied together using CT as common connected to an output filter will yield 18VDC. ** ****ing BULL **** !!!!!!!!!!!!!! I've tried it and it does ** Then explain how every other person on the planet get a different result ?? Using a CT as common halves the voltage from the tranny and so halves the DC voltage as well. My god you are ****ing stupid. ..... Phil |
#27
Posted to sci.electronics.repair
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Power supply question
Jamie What you're referring to is a 12VCT transformer. Connecting either a bridge and not using a center tap or just two diodes across the full secondary with cathodes tied together using CT as common connected to an output filter will yield 18VDC. A 24 V transformer under the same circumstances will produce 36VDC. I've tried it and it does. Lenny. That's not true, I'm afraid. Using the CT as common, and having a diode on each 'hot' limb of the winding will produce half the voltage of hanging a bridge across the same two limbs, and *not* using the centre tap. If you do the same, but continue to use the CT as 'common', then you will get +18v at the "+" terminal of the bridge, and -18v at the "-" terminal ... Arfa |
#28
Posted to sci.electronics.repair
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Power supply question
klem kedidelhopper wrote:
On Feb 27, 6:21 pm, Jamie t wrote: klem kedidelhopper wrote: On Feb 26, 6:39 pm, Jamie et wrote: wrote: On Sunday, February 24, 2013 10:17:29 AM UTC-5, Arfa Daily wrote: "klem kedidelhopper" wrote in message ... On Feb 20, 6:06 pm, amdx wrote: On 2/19/2013 5:01 PM, klem kedidelhopper wrote: On Feb 19, 12:51 am, "Phil Allison" wrote: With a full-wave bridge rectifier, if you use an 8300 uF capacitor, the volts of ripple will equal the amps of load current. (Don Lancaster taught me this.) ** The correct value is 6300uF. Such a cap will drop 1 volt in 6.3mS, the typical discharge time in a full wave rectifier at 60Hz. For 50Hz full wave supplies, the value is 7500uF for 1V ripple at 1 amp. .... Phil This is some great advice. Thank you everyone for all your input. I especially like the diode and Zener ideas. They/re cheap and should work well. I've got lots of diodes around here and I'm going to experiment with them. However after all this I remembered that the transformer is center tapped! At the time, I simply wire nutted the tap, tucked it down under the transformer and forgot about it. How this simple fact and the possibilities it presents slipped my mind is anyone's guess. I've been building this thing in the evenings after my usual work and perhaps I've been tired. The transformer measures 25.2V at 120V line unloaded. Loading the transformer in this fashion will probably unbalance it somewhat and drop the 24V a bit as well but I don't see it as a real problem. I should be able to use one side of the secondary and the tap now get at least 15 -17 VDC out of the bridge and filter, and that will provide a healthier input to my regulator. Lenny No need to unbalance the transformer, just use 2 diodes and use the center tap as negative. See Here, http://metroamp.com/wiki/index.php/F..._Tap_Rectifier Mikek But won't that still give me 36VDC into my regulator? Lenny No, it won't Arfa I looked over what I had previously written and perhaps I didn’t explain this properly. I have a 24VCT transformer. The transformer needs to power 24VAC equipment as well as 12VDC equipment. For the DC circuit I first tried using a bridge directly off the 24V winding. As soon as I connected up the filter cap the DC output went to 35V, which is probably too high to feed my 12V regulator. Several people came up with some great ideas to address this, and I then realized that I had a center tap that was not being used. So I connected my bridge across the center tap and one side of the secondary. This time the 13VAC when FW rectified using the bridge went to about 19VDC, which is a safe input to the regulator. Although this worked, I wasn’t happy about unbalancing the transformer this way so I posted my results. Unless I seriously misunderstood It was suggested here that I come off the full secondary output with two diodes, cathodes tied together, (typical FW rectifier), and use the center tap as my negative return. I didn't think that would make any difference in the output voltage from using a bridge without the center tap however I tried it anyway. As I suspected it would, the DC output again went to 35V when I connected the filter up. I've been playing with power supplies all my life and maybe my age is catching up with me. I guess I just don't understand the explanation of how to get a lower voltage to my DC regulator by what I thought sounded like just configuring the transformer properly. So at the risk of sounding like a complete idiot here can someone please explain this further? Thanks, Lenny Your problem is simple If the 24V AC devices does not come in contact with the common or ground of this supply you have, you can use a 2 diode full wave config. The center tap would be your common for the 12 volt supply, one diode from each outter leg joined together to form a full wave. The diode output alogn with using the center tap as your common will give you 12 * 1.414 volts unloaded. If you need to use a 12 Volt reg, I guess you could do that. Use a LDO type. As for the 24 v AC, the outter legs will supply that to the out board device. Make sure the AC legs do not come in contact with either grd or DC out.. o o | | | | to your 24V AC device | | | | | | | | | | | | + | | --------------+. ,-o---------|-----|-+--+ )|( | | 18DC )|( | +------++ Line Voltage -. ,-+----+| | | === )|( === | | /-\ )|( GND | | | +-------------+-' '+----------o-----|+----+ === GND (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) Unless I missed something, I don't see a problem? Jamie I'm not sure if my last reply worked so I'll try it again. I know that it's very difficult when all we can use here is text but I'm afraid that I just can't understand, (read) your schematic. From you description however it appears to be the FW arrangement that I've already tried and got 35 V out of after I connected up the filter. Is there any way to make your diagram any more readable in this medium? Thanks, Lenny THe FW you tried was a 4 diode bridge, this is a 2 diode full wave config. THe difference being is, the CT (Center tap) is your common, the negative terminal and where the Cathode of the 2 diodes come together are the (+) terminal which will be around 18VDC with Cap attached If you truly do have a 24 volt transformer with CT, this means you'll get 12 Volts from each outer leg with respect to the CT. Because they are out of phase with each other (180), this is a split phase configuration, like seen in residential pole pigs in the USA. If you have done this and gotten 36 volts, then you actually have a 48V transformer with CT Jamie What you're referring to is a 12VCT transformer. Connecting either a bridge and not using a center tap or just two diodes across the full secondary with cathodes tied together using CT as common connected to an output filter will yield 18VDC. A 24 V transformer under the same circumstances will produce 36VDC. I've tried it and it does. Lenny. absolutely not, you are greatly mistaken or you don't know what you have for a transformer. THe transformer is spec'ed out via its outer legs, the highest voltage. The CT is the voltage divider. when you use the CT as your common, the supply will yield only half of the rated voltage of that transformer and is when you use only 2 diodes from the outer legs to form a full wave into a single node where this becomes the (+) terminal. With a real 24V Transformer with CT and using the CT as your common (-) terminal, you will get 12*1.414 = 16.968-0.650 = 16.318VDC at the peak of a marginal ripple. You have your logic mixed up Jamie |
#29
Posted to sci.electronics.repair
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Power supply question
On Feb 28, 7:21*pm, Jamie
t wrote: klem kedidelhopper wrote: On Feb 27, 6:21 pm, Jamie t wrote: klem kedidelhopper wrote: On Feb 26, 6:39 pm, Jamie et wrote: wrote: On Sunday, February 24, 2013 10:17:29 AM UTC-5, Arfa Daily wrote: "klem kedidelhopper" wrote in message ... On Feb 20, 6:06 pm, amdx wrote: On 2/19/2013 5:01 PM, klem kedidelhopper wrote: On Feb 19, 12:51 am, "Phil Allison" wrote: With a full-wave bridge rectifier, if you use an 8300 uF capacitor, the volts of ripple will equal the amps of load current. *(Don Lancaster taught me this.) ** The correct value is 6300uF. Such a cap will drop 1 volt in 6.3mS, the typical discharge time in a full wave rectifier at 60Hz. For 50Hz full wave supplies, the value is 7500uF for 1V ripple at 1 amp. .... *Phil This is some great advice. Thank you everyone for all your input.. I especially like the diode and Zener ideas. They/re cheap and should work well. I've got lots of diodes around here and I'm going to experiment with them. However after all this I remembered that the transformer is center tapped! *At the time, I simply wire nutted the tap, tucked it down under the transformer and forgot about it. How this simple fact and the possibilities it presents slipped my mind is anyone's guess. I've been building this thing in the evenings after my usual work and perhaps I've been tired. The transformer measures 25.2V at 120V line unloaded. Loading the transformer in this fashion will probably unbalance it somewhat and drop the 24V a bit as well but I don't see it as a real problem. I should be able to use one side of the secondary and the tap now get at least 15 -17 VDC out of the bridge and filter, and that will provide a healthier input to my regulator. Lenny No need to unbalance the transformer, just use 2 diodes and use the center tap as negative. See Here, http://metroamp.com/wiki/index.php/F..._Tap_Rectifier * * * * * * * * * * * * * * *Mikek But won't that still give me 36VDC into my regulator? Lenny No, it won't Arfa I looked over what I had previously written and perhaps I didn’t explain this properly. I have a 24VCT transformer. The transformer needs to power 24VAC equipment as well as 12VDC equipment. For the DC circuit I first tried using a bridge directly off the 24V winding. As soon as I connected up the filter cap the DC output went to 35V, which is probably too high to feed my 12V regulator. Several people came up with some great ideas to address this, and I then realized that I had a center tap that was not being used. So I connected my bridge across the center tap and one side of the secondary. This time the 13VAC when FW rectified using the bridge went to about 19VDC, which is *a safe input to the regulator. Although this worked, I wasn’t happy about unbalancing the transformer this way so I posted my results. Unless I seriously misunderstood It was suggested here that I come off the full secondary output with two diodes, cathodes tied together, (typical FW rectifier), and use the center tap as my negative return. I didn't think that would make any difference in the output voltage from using a bridge without the center tap however I tried it anyway. As I suspected it would, the DC output again went to 35V when I connected the filter up. I've been playing with power supplies all my life and maybe my age is catching up with me. I guess I just don't understand the explanation of how to get a lower voltage to my DC regulator by what I thought sounded like just configuring the transformer properly. So at the risk of sounding like a complete idiot here can someone please explain this further? Thanks, Lenny Your problem is simple *If the 24V AC devices does not come in contact with the common or ground of this supply you have, you can use a 2 diode full wave config. *The center tap would be your common for the 12 volt supply, one diode from each outter leg joined together to form a full wave. The diode output alogn with using the center tap as your common will give you 12 * 1.414 volts unloaded. If you need to use a 12 Volt reg, I guess you could do that. Use a LDO type. As for the 24 v AC, the outter legs will supply that to the out board device. Make sure the AC legs do not come in contact with either grd or DC out.. * * * * * * * * * * * * * * * * o * * * *o * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * | * * * * | to your 24V AC device * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * | * * * * | * * * * * * * * * * * * * * * * | * * * * | * * * * * * + * * * * * * * * * | * * * * | * * * * * * *--------------+. ,-o---------|-----|-+--+ * * * * * * * * * * * * * * )|( * * * * * | * * * * * | * *18DC * * * * * * * * * * * * * * )|( * * * * * | * * * * * +------++ * * * *Line Voltage * * * *-. ,-+----+| * | * * * * * | * * === * * * * * * * * * * * * * * )|( * * *=== *| * * * * * | * * /-\ * * * * * * * * * * * * * * )|( * * *GND *| * * * * * | * * *| * * * * * * +-------------+-' '+----------o-----|+----+ * *=== * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * GND (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) Unless I missed something, I don't see a problem? Jamie I'm not sure if my last reply worked so I'll try it again. I know that it's very difficult when all we can use here is text but I'm afraid that I just can't understand, (read) your schematic. From you description however it appears to be the FW arrangement that I've already tried and got 35 V out of after I connected up the filter. Is there any way to make your diagram any more readable in this medium? Thanks, Lenny *THe FW you tried was a 4 diode bridge, this is a 2 diode full wave config. * THe difference being is, the CT (Center tap) is your common, the negative terminal and where the Cathode of the 2 diodes come together are the (+) terminal which will be around 18VDC with Cap attached *If you truly do have a 24 volt transformer with CT, this means you'll get 12 Volts from each outer leg with respect to the CT. Because they are out of phase with each other (180), this is a split phase configuration, like seen in residential pole pigs in the USA. *If you have done this and gotten 36 volts, then you actually have a 48V transformer with CT Jamie What you're referring to is a 12VCT transformer. Connecting either a bridge and not using a center tap or just two diodes across the full secondary with cathodes tied together using CT *as common connected to an output filter will yield 18VDC. A 24 V transformer under the same circumstances will produce 36VDC. I've tried it and it does. Lenny. absolutely not, you are greatly mistaken or you don't know what you have for a transformer. * *THe transformer is spec'ed out via its outer legs, the highest voltage. The CT is the voltage divider. when you use the CT as your common, the supply will yield only half of the rated voltage of that transformer and is when you use only 2 diodes from the outer legs to form a full wave into a single node where this becomes the (+) terminal. * *With a real 24V Transformer with CT and using the CT as your common (-) terminal, you will get 12*1.414 = 16.968-0.650 = 16.318VDC at the peak of a marginal ripple. * *You have your logic mixed up Jamie What I decided to do is use the full secondary and employ the two 6.8V zeners in series with the cap. That arrangement gives me 21V out of my power supply to feed the 12V regulator. As far as I can tell the other methods would be using the center tap and one side of the transformer, a method which I didn't want to use. I tried this full secondary arrangement with a 1.2A load and the 21V across the zeners holds pretty steady. I have a nice heat sink for the two diodes, (they will be insulated) that will be going into the box as well. Thanks everyone who advised and helped me on this project. Lenny |
#30
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Power supply question
"klem kedidelhopper" What I decided to do is use the full secondary and employ the two 6.8V zeners in series with the cap. That arrangement gives me 21V out of my power supply to feed the 12V regulator. ** He sure is one stubborn SOB - ain't he? ..... Phil |
#31
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Power supply question
"Phil Allison" wrote in message ... "klem kedidelhopper" What I decided to do is use the full secondary and employ the two 6.8V zeners in series with the cap. That arrangement gives me 21V out of my power supply to feed the 12V regulator. ** He sure is one stubborn SOB - ain't he? .... Phil Well, as long as it works ok for him, and he understands it, I guess it's a result in the end ... Arfa |
#32
Posted to sci.electronics.repair
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Power supply question
"Arfa Daily" "Phil Allison" "klem kedidelhopper" What I decided to do is use the full secondary and employ the two 6.8V zeners in series with the cap. That arrangement gives me 21V out of my power supply to feed the 12V regulator. ** He sure is one stubborn SOB - ain't he? Well, as long as it works ok for him, and he understands it, I guess it's a result in the end ... ** All the fool had to do was LOOK at his wiring and spot the mistake. The CT wire was swapped with one of the ends. FFS, what a annoying moron. |
#33
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Power supply question
Phallus'n wrote:
** He sure is one stubborn SOB - ain't he? .... Phil Snort.... No one is more stubborn than Phallus'n. No one. Phil stubbornly hangs on to an argument when he's been long proven wrong. His stubbornness is so well known in fact that he was given a guest cameo on a sitcom. He's the one on the right. Enjoy: http://www.youtube.com/watch?v=fqs9DYisSsg |
#34
Posted to sci.electronics.repair
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Power supply question
klem kedidelhopper wrote:
On Feb 28, 7:21 pm, Jamie t wrote: klem kedidelhopper wrote: On Feb 27, 6:21 pm, Jamie t wrote: klem kedidelhopper wrote: On Feb 26, 6:39 pm, Jamie t wrote: wrote: On Sunday, February 24, 2013 10:17:29 AM UTC-5, Arfa Daily wrote: "klem kedidelhopper" wrote in message ... On Feb 20, 6:06 pm, amdx wrote: On 2/19/2013 5:01 PM, klem kedidelhopper wrote: On Feb 19, 12:51 am, "Phil Allison" wrote: With a full-wave bridge rectifier, if you use an 8300 uF capacitor, the volts of ripple will equal the amps of load current. (Don Lancaster taught me this.) ** The correct value is 6300uF. Such a cap will drop 1 volt in 6.3mS, the typical discharge time in a full wave rectifier at 60Hz. For 50Hz full wave supplies, the value is 7500uF for 1V ripple at 1 amp. .... Phil This is some great advice. Thank you everyone for all your input.. I especially like the diode and Zener ideas. They/re cheap and should work well. I've got lots of diodes around here and I'm going to experiment with them. However after all this I remembered that the transformer is center tapped! At the time, I simply wire nutted the tap, tucked it down under the transformer and forgot about it. How this simple fact and the possibilities it presents slipped my mind is anyone's guess. I've been building this thing in the evenings after my usual work and perhaps I've been tired. The transformer measures 25.2V at 120V line unloaded. Loading the transformer in this fashion will probably unbalance it somewhat and drop the 24V a bit as well but I don't see it as a real problem. I should be able to use one side of the secondary and the tap now get at least 15 -17 VDC out of the bridge and filter, and that will provide a healthier input to my regulator. Lenny No need to unbalance the transformer, just use 2 diodes and use the center tap as negative. See Here, http://metroamp.com/wiki/index.php/F..._Tap_Rectifier Mikek But won't that still give me 36VDC into my regulator? Lenny No, it won't Arfa I looked over what I had previously written and perhaps I didn’t explain this properly. I have a 24VCT transformer. The transformer needs to power 24VAC equipment as well as 12VDC equipment. For the DC circuit I first tried using a bridge directly off the 24V winding. As soon as I connected up the filter cap the DC output went to 35V, which is probably too high to feed my 12V regulator. Several people came up with some great ideas to address this, and I then realized that I had a center tap that was not being used. So I connected my bridge across the center tap and one side of the secondary. This time the 13VAC when FW rectified using the bridge went to about 19VDC, which is a safe input to the regulator. Although this worked, I wasn’t happy about unbalancing the transformer this way so I posted my results. Unless I seriously misunderstood It was suggested here that I come off the full secondary output with two diodes, cathodes tied together, (typical FW rectifier), and use the center tap as my negative return. I didn't think that would make any difference in the output voltage from using a bridge without the center tap however I tried it anyway. As I suspected it would, the DC output again went to 35V when I connected the filter up. I've been playing with power supplies all my life and maybe my age is catching up with me. I guess I just don't understand the explanation of how to get a lower voltage to my DC regulator by what I thought sounded like just configuring the transformer properly. So at the risk of sounding like a complete idiot here can someone please explain this further? Thanks, Lenny Your problem is simple If the 24V AC devices does not come in contact with the common or ground of this supply you have, you can use a 2 diode full wave config. The center tap would be your common for the 12 volt supply, one diode from each outter leg joined together to form a full wave. The diode output alogn with using the center tap as your common will give you 12 * 1.414 volts unloaded. If you need to use a 12 Volt reg, I guess you could do that. Use a LDO type. As for the 24 v AC, the outter legs will supply that to the out board device. Make sure the AC legs do not come in contact with either grd or DC out.. o o | | | | to your 24V AC device | | | | | | | | | | | | + | | --------------+. ,-o---------|-----|-+--+ )|( | | 18DC )|( | +------++ Line Voltage -. ,-+----+| | | === )|( === | | /-\ )|( GND | | | +-------------+-' '+----------o-----|+----+ === GND (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) Unless I missed something, I don't see a problem? Jamie I'm not sure if my last reply worked so I'll try it again. I know that it's very difficult when all we can use here is text but I'm afraid that I just can't understand, (read) your schematic. From you description however it appears to be the FW arrangement that I've already tried and got 35 V out of after I connected up the filter. Is there any way to make your diagram any more readable in this medium? Thanks, Lenny THe FW you tried was a 4 diode bridge, this is a 2 diode full wave config. THe difference being is, the CT (Center tap) is your common, the negative terminal and where the Cathode of the 2 diodes come together are the (+) terminal which will be around 18VDC with Cap attached If you truly do have a 24 volt transformer with CT, this means you'll get 12 Volts from each outer leg with respect to the CT. Because they are out of phase with each other (180), this is a split phase configuration, like seen in residential pole pigs in the USA. If you have done this and gotten 36 volts, then you actually have a 48V transformer with CT Jamie What you're referring to is a 12VCT transformer. Connecting either a bridge and not using a center tap or just two diodes across the full secondary with cathodes tied together using CT as common connected to an output filter will yield 18VDC. A 24 V transformer under the same circumstances will produce 36VDC. I've tried it and it does. Lenny. absolutely not, you are greatly mistaken or you don't know what you have for a transformer. THe transformer is spec'ed out via its outer legs, the highest voltage. The CT is the voltage divider. when you use the CT as your common, the supply will yield only half of the rated voltage of that transformer and is when you use only 2 diodes from the outer legs to form a full wave into a single node where this becomes the (+) terminal. With a real 24V Transformer with CT and using the CT as your common (-) terminal, you will get 12*1.414 = 16.968-0.650 = 16.318VDC at the peak of a marginal ripple. You have your logic mixed up Jamie What I decided to do is use the full secondary and employ the two 6.8V zeners in series with the cap. That arrangement gives me 21V out of my power supply to feed the 12V regulator. As far as I can tell the other methods would be using the center tap and one side of the transformer, a method which I didn't want to use. I tried this full secondary arrangement with a 1.2A load and the 21V across the zeners holds pretty steady. I have a nice heat sink for the two diodes, (they will be insulated) that will be going into the box as well. Thanks everyone who advised and helped me on this project. Lenny Until one of your zener diodes short out (a zener will eventually short out due to inrush current issues is my guess) and you then punch around 19V to the circuit that wants 12....not a good design as a result, more of a hack. John :-#(# |
#35
Posted to sci.electronics.repair
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Power supply question
"John Robertson" wrote in message ... klem kedidelhopper wrote: On Feb 28, 7:21 pm, Jamie t wrote: klem kedidelhopper wrote: On Feb 27, 6:21 pm, Jamie t wrote: klem kedidelhopper wrote: On Feb 26, 6:39 pm, Jamie t wrote: wrote: On Sunday, February 24, 2013 10:17:29 AM UTC-5, Arfa Daily wrote: "klem kedidelhopper" wrote in message ... On Feb 20, 6:06 pm, amdx wrote: On 2/19/2013 5:01 PM, klem kedidelhopper wrote: On Feb 19, 12:51 am, "Phil Allison" wrote: With a full-wave bridge rectifier, if you use an 8300 uF capacitor, the volts of ripple will equal the amps of load current. (Don Lancaster taught me this.) ** The correct value is 6300uF. Such a cap will drop 1 volt in 6.3mS, the typical discharge time in a full wave rectifier at 60Hz. For 50Hz full wave supplies, the value is 7500uF for 1V ripple at 1 amp. .... Phil This is some great advice. Thank you everyone for all your input.. I especially like the diode and Zener ideas. They/re cheap and should work well. I've got lots of diodes around here and I'm going to experiment with them. However after all this I remembered that the transformer is center tapped! At the time, I simply wire nutted the tap, tucked it down under the transformer and forgot about it. How this simple fact and the possibilities it presents slipped my mind is anyone's guess. I've been building this thing in the evenings after my usual work and perhaps I've been tired. The transformer measures 25.2V at 120V line unloaded. Loading the transformer in this fashion will probably unbalance it somewhat and drop the 24V a bit as well but I don't see it as a real problem. I should be able to use one side of the secondary and the tap now get at least 15 -17 VDC out of the bridge and filter, and that will provide a healthier input to my regulator. Lenny No need to unbalance the transformer, just use 2 diodes and use the center tap as negative. See Here, http://metroamp.com/wiki/index.php/F..._Tap_Rectifier Mikek But won't that still give me 36VDC into my regulator? Lenny No, it won't Arfa I looked over what I had previously written and perhaps I didn’t explain this properly. I have a 24VCT transformer. The transformer needs to power 24VAC equipment as well as 12VDC equipment. For the DC circuit I first tried using a bridge directly off the 24V winding. As soon as I connected up the filter cap the DC output went to 35V, which is probably too high to feed my 12V regulator. Several people came up with some great ideas to address this, and I then realized that I had a center tap that was not being used. So I connected my bridge across the center tap and one side of the secondary. This time the 13VAC when FW rectified using the bridge went to about 19VDC, which is a safe input to the regulator. Although this worked, I wasn’t happy about unbalancing the transformer this way so I posted my results. Unless I seriously misunderstood It was suggested here that I come off the full secondary output with two diodes, cathodes tied together, (typical FW rectifier), and use the center tap as my negative return. I didn't think that would make any difference in the output voltage from using a bridge without the center tap however I tried it anyway. As I suspected it would, the DC output again went to 35V when I connected the filter up. I've been playing with power supplies all my life and maybe my age is catching up with me. I guess I just don't understand the explanation of how to get a lower voltage to my DC regulator by what I thought sounded like just configuring the transformer properly. So at the risk of sounding like a complete idiot here can someone please explain this further? Thanks, Lenny Your problem is simple If the 24V AC devices does not come in contact with the common or ground of this supply you have, you can use a 2 diode full wave config. The center tap would be your common for the 12 volt supply, one diode from each outter leg joined together to form a full wave. The diode output alogn with using the center tap as your common will give you 12 * 1.414 volts unloaded. If you need to use a 12 Volt reg, I guess you could do that. Use a LDO type. As for the 24 v AC, the outter legs will supply that to the out board device. Make sure the AC legs do not come in contact with either grd or DC out.. o o | | | | to your 24V AC device | | | | | | | | | | | | + | | --------------+. ,-o---------|-----|-+--+ )|( | | 18DC )|( | +------++ Line Voltage -. ,-+----+| | | === )|( === | | /-\ )|( GND | | | +-------------+-' '+----------o-----|+----+ === GND (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) Unless I missed something, I don't see a problem? Jamie I'm not sure if my last reply worked so I'll try it again. I know that it's very difficult when all we can use here is text but I'm afraid that I just can't understand, (read) your schematic. From you description however it appears to be the FW arrangement that I've already tried and got 35 V out of after I connected up the filter. Is there any way to make your diagram any more readable in this medium? Thanks, Lenny THe FW you tried was a 4 diode bridge, this is a 2 diode full wave config. THe difference being is, the CT (Center tap) is your common, the negative terminal and where the Cathode of the 2 diodes come together are the (+) terminal which will be around 18VDC with Cap attached If you truly do have a 24 volt transformer with CT, this means you'll get 12 Volts from each outer leg with respect to the CT. Because they are out of phase with each other (180), this is a split phase configuration, like seen in residential pole pigs in the USA. If you have done this and gotten 36 volts, then you actually have a 48V transformer with CT Jamie What you're referring to is a 12VCT transformer. Connecting either a bridge and not using a center tap or just two diodes across the full secondary with cathodes tied together using CT as common connected to an output filter will yield 18VDC. A 24 V transformer under the same circumstances will produce 36VDC. I've tried it and it does. Lenny. absolutely not, you are greatly mistaken or you don't know what you have for a transformer. THe transformer is spec'ed out via its outer legs, the highest voltage. The CT is the voltage divider. when you use the CT as your common, the supply will yield only half of the rated voltage of that transformer and is when you use only 2 diodes from the outer legs to form a full wave into a single node where this becomes the (+) terminal. With a real 24V Transformer with CT and using the CT as your common (-) terminal, you will get 12*1.414 = 16.968-0.650 = 16.318VDC at the peak of a marginal ripple. You have your logic mixed up Jamie What I decided to do is use the full secondary and employ the two 6.8V zeners in series with the cap. That arrangement gives me 21V out of my power supply to feed the 12V regulator. As far as I can tell the other methods would be using the center tap and one side of the transformer, a method which I didn't want to use. I tried this full secondary arrangement with a 1.2A load and the 21V across the zeners holds pretty steady. I have a nice heat sink for the two diodes, (they will be insulated) that will be going into the box as well. Thanks everyone who advised and helped me on this project. Lenny Until one of your zener diodes short out (a zener will eventually short out due to inrush current issues is my guess) and you then punch around 19V to the circuit that wants 12....not a good design as a result, more of a hack. John :-#(# Well then you want another protection Zener shunted on the 12v line. Gareth. |
#36
Posted to sci.electronics.repair
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Power supply question
On Wed, 27 Feb 2013 21:24:41 -0800 (PST), klem kedidelhopper
wrote: *As for the 24 v AC, the outter legs will supply that to the out board device. Make sure the AC legs do not come in contact with either grd or DC out.. * * * * * * * * * * * * * * * * *o * * * *o * * * * * * * * * * * * * * * * *| * * * * | * * * * * * * * * * * * * * * * *| * * * * | to your 24V AC device * * * * * * * * * * * * * * * * *| * * * * | * * * * * * * * * * * * * * * * *| * * * * | * * * * * * * * * * * * * * * * *| * * * * | * * * * * * * * * * * * * * * * *| * * * * | * * * * * * * * * * * * * * * * *| * * * * | * * * * * * * * * * * * * * * * *| * * * * | * * * * * * *+ * * * * * * * * * | * * * * | * * * * * * * --------------+. ,-o---------|-----|-+--+ * * * * * * * * * * * * * * *)|( * * * * * | * * * * * | * *18DC * * * * * * * * * * * * * * *)|( * * * * * | * * * * * +------++ * * * * Line Voltage * * * *-. ,-+----+| * | * * * * * | * * === * * * * * * * * * * * * * * *)|( * * *=== *| * * * * * | * * /-\ * * * * * * * * * * * * * * *)|( * * *GND *| * * * * * | * * *| * * * * * * *+-------------+-' '+----------o-----|+----+ * *=== * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *GND (created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de) *Unless I missed something, I don't see a problem? Jamie I'm not sure if my last reply worked so I'll try it again. I know that it's very difficult when all we can use here is text but I'm afraid that I just can't understand, (read) your schematic. From you description however it appears to be the FW arrangement that I've already tried and got 35 V out of after I connected up the filter. Is there any way to make your diagram any more readable in this medium? Thanks, Lenny * THe FW you tried was a 4 diode bridge, this is a 2 diode full wave config. * *THe difference being is, the CT (Center tap) is your common, the negative terminal and where the Cathode of the 2 diodes come together are the (+) terminal which will be around 18VDC with Cap attached * If you truly do have a 24 volt transformer with CT, this means you'll get 12 Volts from each outer leg with respect to the CT. Because they are out of phase with each other (180), this is a split phase configuration, like seen in residential pole pigs in the USA. * If you have done this and gotten 36 volts, then you actually have a 48V transformer with CT Jamie What you're referring to is a 12VCT transformer. Connecting either a bridge and not using a center tap or just two diodes across the full secondary with cathodes tied together using CT as common connected to an output filter will yield 18VDC. A 24 V transformer under the same circumstances will produce 36VDC. I've tried it and it does. Lenny. Two questions: Do you have LTSpice? Can you read alt.binaries.schematics.electronic? If the answer in no in both cases, get LTSpice. The .asc files are very handy for this kind of discussion. ?-) |
#37
Posted to sci.electronics.repair
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Power supply question
Until one of your zener diodes short out (a zener will eventually short out due to inrush current issues is my guess) and you then punch around 19V to the circuit that wants 12....not a good design as a result, more of a hack. John :-#(# Yebbut, the zeners are not dropping the supply to 12v. They are *reducing* the input supply to a full blown 12 v regulator sub-circuit that the OP already has. Further, that regulator is expecting smooth DC in, so probably only has a few tens of uF hung across its input, for decoupling purposes, so there will not be any serious inrush current through the zeners. Given that fact, there is no reason why the zeners should ever fail, particularly as they are high wattage stud types anyway. The technique of placing zeners in series with voltages that you want to reduce by a steady and relatively current-independent amount, is well known, and not uncommon in commercial designs. Arfa |
#38
Posted to sci.electronics.repair
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Power supply question
"John-Del" wrote in message ... Phallus'n wrote: ** He sure is one stubborn SOB - ain't he? .... Phil Snort.... No one is more stubborn than Phallus'n. No one. Phil stubbornly hangs on to an argument when he's been long proven wrong. His stubbornness is so well known in fact that he was given a guest cameo on a sitcom. He's the one on the right. Enjoy: http://www.youtube.com/watch?v=fqs9DYisSsg But when he's right, he's right. And in this case, he is ... Arfa |
#39
Posted to sci.electronics.repair
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Power supply question
But when he's right, he's right. And in this case, he is ... Arfa That's not the point.. Phil chides the OP for being stubborn, but all one could accuse him of is being wrong. I guess it's the internet bullying that makes Phil such a dick, and I'm sure he's a bigger tool in person. Would he act out in such a manner if he was standing directly in front of the OP? I doubt it. Over the years, I've discovered that most bullys are spineless, who hide behind a false facade of toughness (until called on it), or behind a keyboard. If I knew that Phil acted the same way in person as he does on the internet, I might even like the guy, and buy him a beer (after pounding the snot out of him). But I'd bet almost anything that if challenged, he'd run home to mommy and hide in her basement. |
#40
Posted to sci.electronics.repair
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Power supply question
"John-Del" = ****WIT TROLL But when he's right, he's right. And in this case, he is ... Arfa That's not the point.. Phil chides the OP for being stubborn, but all one could accuse him of is being wrong. ** Completely and utterly WRONG !!! **** OFF TO HELL - YOU RETARDED ****ING NET STALKER .... Phil |
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